What Is Battery Capacity?

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If you’re only just beginning to learn about batteries and you only want to know the bare-bone basics of what battery capacity means, then you’re in the right place!

Let’s look at a simple definition of this mysterious “battery capacity” in this easy-to-read post!

But before you can understand what battery capacity is, let’s look at simple electrical circuit and go from there. (You might think knowing all this preliminary stuff is worthless, but at the end of this post you’ll understand why you had to learn this other basic stuff first).

Basic Electrical Circuit

The simplest one-sentence definition of an electric circuit (or electrical circuit) is it’s a closed-loop that carries electricity.

The simplest electric circuit has 3 things connected together, which include:

  1. a power source,
  2. a conductor,
  3. and a load.
A basic electric circuit.

Power Source

The power source is the part of the circuit that produces or stores electricity. For example, both a generator and a solar panel produce electricity, while a battery stores electricity.


The conductor is the part of the circuit that allows the flow of the electrical current. The most common example of a conductor is a wire.


The load is the part of the electric circuit that receives electricity for performing some sort of action. For example, a light bulb will receive electricity to produce light.

Electrons: Negative to Positive

Electrons are very small particles of matter that have a negative charge of electricity.

To have a complete circuit, electrons from the power source have to travel from its negative side, through the path of the circuit (which includes the conductor and the load), and then back to the power source through its positive side.

Electrons moving from the negative side to the positive side of the power source.

You can think about a circuit like a racetrack. The cars (electrons) have to go all the way around and back to the starting point (the power source). If you don’t have a closed-loop, no electricity can flow around and around and around the circuit.

Electrical Current

The simplest definition of an electrical current (also called electric current) is it’s the flow of electrons in a circuit.

More specifically, the electric current is the unit of how many electrons move past a given point per second through a conductor.

This current is measured in amps/ampere (A).

Amps are the unit of how many electrons move past a given point per second through a conductor

What Is Battery Capacity?

So, now that you know all the above, understanding the bare bone basics of battery capacity will be super simple…

Battery capacity is the amount of current that’s released from a battery over a period of time. In other words, battery capacity means the actual quantity of electricity that you can extract out of a battery from when it’s fully charged to fully discharged.

Battery capacity is usually expressed in units of amp-hours (Ah) for things like deep-cycle batteries (like the ones you use in a solar power system).

Amp-Hour (Ah) = Amps x Hours

So, simply put, amp-hour is measuring how many electrons move past a given point per hour through a conductor.

Battery Capacity Decreases Over Time

Once you’ve used a rechargable battery for awhile, it’ll start dying faster. So, let’s say a battery used to last you 9 hours. After awhile, that same battery might only last you an hour.

This happens because all batteries start to degrade from the moment you start using it. And then, eventually, you’ll have to replace that battery with a new one.